Real-world COVID-19 vaccine effectiveness in Zimbabwe: A test-negative case-control study

Abstract

Background: COVID-19 vaccination is critical in sub-Saharan Africa to reduce the disease burden. This study assessed real-world vaccine effectiveness (VE) in Zimbabwe.

Aim: To determine COVID-19 VE and factors associated with disease severity and mortality in Zimbabwe.

Setting: The study setting comprised a test-negative case-control study across health facilities in Harare and Bulawayo (May 2023 – August 2023).

Methods: Adults (≥ 18 years) were recruited from COVID-19 registers (1:1 case-control; matched by sex, age and clinic visit date). Telephone interviews assessed vaccination status, disease severity (cases) and comorbidities. Conditional logistic regression estimated VE (1 – odds ratio*100), with stratification by age and comorbidities. Ordinal and simple logistic regression analysed factors associated with disease severity and vaccination–variant relationships.

Results: Overall vaccination coverage was 38% (fully vaccinated including boosters), with 62% unvaccinated. The median age was 38 years (interquartile range [IQR]: 30–50) with more females (n = 352). Overall VE against any COVID-19 infection was 32.2% (95% CI: 8.9, 49.5). Older age (45+ years) and chronic conditions were associated with increased hospitalisation risk. Among cases, hospitalisation rate was 34.8% (n = 174/500) and COVID-19-related mortality rate was 11.6% (n = 58/500).

Conclusion: This study found a moderate VE of COVID-19 vaccines in Zimbabwe, potentially influenced by age, comorbidities and variants. We highlight the need for targeted vaccination strategies and public health measures informed by these findings.

Contribution: This research informs public health strategies to optimise vaccination efforts and improve health outcomes across Africa, aligning with the journal’s focus on public health issues.